Underwater listening aid for submerged personnel



UNDERWATER LISTENING AID FOR SUBMERGED PERSONNEL Filed July 23, 1946JOHN M. IDE

. to. the difference in sound velocities in air and Water.

, 3,296,582 I UNDERWATER LIS IENING AID FOR SUBMERGED PERSONNEL John M.Ide,iAlexandria, Va. (2332 Massachusetts Ave., NW., Washington, D.C.20008) Filed July 23,1946, Ser. No. 685,631 Claims. (Cl. 340.-5)

. coming from any direction except straight ahead reach the: two ears atslightly different times. i can estimate, bearingsto a few degrees,corresponding to time differencos of the order of one-one hundred thou-In air, the ears sandths of a second. With the ears submerged, thedirection of underwater sound should be perceived in the same manner asin air, but the accuracy should be lower owing In water the situation isfurthercomplicated by the masking effect of sound received by boneconduction through various parts of the head. Sound received throughareas midway between the ears, particularly the top and back of thehead, has no directional character but does contribute to the overallloudness.

Investigation has shown that submerged bone conduction hearing andsubmerged eardrum hearing are of the same. order. ,of sensitivity. Itmay be expected that effects of increasing depth will further attenuatethe eardrum hearing. sensitivity, owing to the unbalance of staticpressure on the drum. Since the bone conduction hearing is not so,affected, the directional indication usually arising from a binauraleffectbecomes progressively lost, and tests have shown that, to asubmerged person the soundsource appears more or less directly overheadat all times. Afirst object of the present invention is to remedy this,and to restore a binaural effect from which a direction indication maybe gained by providing means for acousi which will be simple, and lightin construction.

AprincipaLfeature of this invention is the use of a strip of materialhaving acoustical impedance sharply different from that of the seawater,and in acoustic contact, with the central part of the bony structure ofthe head, in a helmet of light construction closely fitting the head.This and other features of the invention will become more apparent; fromthe following detailed description taken together with the accompanyingdrawing, wherein the single figure: is a perspective of a helmetconstructed according to the principles of the present invention.

There is depicted in the figure a helmet of fabric or other lightmaterial having portions adapted to extend over and fit the sides of thehead, and a centrally disposed portion 11. The portion 11 extends fromfront to back of the :helmet, and when worn willthus extend from thebase of the skull to theforehead. The portion 11 forms an outer.covering for a sponge rubber strip 12 which provides a sharp acousticmismatch with the seawater owing to the great number of air bubbles itcontains. A

1 piece of fabric or light material 13 is sewed in to form a 1 pocket;containing the sponge rubber strip 12. The

stitches 14 indicate the line of the sewing. The portions 10 have holes15 cut through so that the ears may be free.

United States Patent C) ice 3,296,582 Patented Jan. 3, 1967 18 suitablyspaced, provided means for securing the helmet to the head of thewearer. The size of the rubber strip 12, while not critical, has beenfound to affect the effective hearing sensitivity considerably. Asubstantially uniform width of four inches, with a length which extendsfrom the forehead to the base of the skull, has been found to beadequate.

Any suitable material having a sharp mismatch of acoustical impedancewith that of the seawater can be substituted for the sponge rubber. Forexample, an inflated diaphragm or air cell fitted into the section 11would have substantially the same effect. The sponge rubber has beenfound to withstand much use without appreciable deterioration.

An example of a direct application of these principles occurs in asystem of underwater navigation for swimmers in underwater demolitionteams or commando type operations. For beach reconnaissance which mustbe conducted with a large measure of secrecy, a small boat equipped witha suitable underwater sound source may be positioned in a known locationoffshore. Swimmers equipped with helmets as herein described are sentforth from the boat, and then are able to locate beach characteristics,obstacles in the approaches, etc., by orientating themselves withrespect to the sound source, even though entirely submerged. Inaddition, this system provides a homing signal for expediting the returnof the swimmers to the boa-t. Interruption or modulation of the soundsource may be used as a danger signal or to impart information.Directional properties of an underwater sound source may be used toselectively guide an individual swimmer or group of swimmers down thebeam in a special angular sector. In this way a special sector of beachmay be investigated or obstacles avoided. This has the added advantageof even more security than the non-directional sound source affords. Itis easy to see that multiplication of these systems will furnish amethod of keeping formation, or of guiding a boat to or from a soundsource. Such navigating procedures have been found to be effectivedespite ocean currents. The inherent simplicity and lightness of theequipment required to effect such operations allow their impromptu andextended performance under a great variety of circumstances.

No attempt has been made here to exhaustively point out or cover all thefeatures or applications of the present invention. Many others thanthose described will be apparent to persons skilled in the art. Thescope of the invention is to be defined in the following claims.

What is claimed is:

1. An underwater listening device for sub-merged personnel, comprising astrip of material having a substantially uniform width and an acousticimpedance lower than that of water arranged to extend fore and aft alongthe top of the head of a person substantially from the forehead to thebase of the skull and limited in its lateral extent to omit coverage ofthe ears and sides of the head, and means for holding said stripinposition.

2. A listening aid for underwater navigating personnel comprising a hoodof relatively thin light material adapted to be worn on the head andcarrying a relatively thick central portion in the form of a thickenedstrip of material having a sharp mismatch of acoustical impedance withthat of water extending fore and aft from the forehead to the base ofthe skull and extending laterally approximately two inches from thecenter of the head toward each car over substantially the entire lengthof the strip.

3. A device for enhancing the underwater binaural hearing of a submergedhuman observer comprising, isolating means for acoustically dampingunderwater sound waves at the outer surface of the head of saidobserver, and positioning means maintaining contact between saidisolating means and the head of the observer only over a 3 4 narrowcontinuous central portion of said outer surface 1,394,482 10/ 1921Fessenden 1810.51 from the forehead to the base of the skull which isnearly 1,547,574 7/1925 Fay 1131-05 1 uniform in Width. 1,594,174 7/1926Hart 2-3 4. The device according to claim 3 wherein said isolat-1,810,655 6/ 1931 Haskillg 8 ing means comprises a water vresistantsolid having at 5 1,836,551 11/1932 101165 least one pocket of gastrapped therein. 1, 1 11/1932 Shehter 1810.51 5. The device according toclaim 3 wherein said posi- 2,140,716 12/1938 Pryale tioning meanscomprises a hood of lightweight fabric 2,296,335 9/ 1942 y t h h th l t'v W C a mg means 18 aflmhed 10 CHESTER L. JUSTUS, Primary Examiner.

References Cited by the Examiner CARL w. ROBINSON, DAVID GALVIN,Examiners. UNITED STATES PATENTS NORMAN H. EVANS, FREDERICK M. STRADER,964,380 7/1910 Bowlker 18 1-0-51 P. H. BLAUSTEIN, T. D. JENNINGS, R. A.

1,080,690 12/ 1913 Hipkiss 23 1 FARLEY, Assistant Examiners.

1. AN UNDERWATER LISTENING DEVICE FOR SUBMERGED PERSONNEL, COMPRISING ASTRIP OF MATERIAL HAVING A SUBSTANTIALLY UNIFORM WIDTH AND AN ACOUSTICIMPEDANCE LOWER THAN THAT OF WATER ARRANGED TO EXTEND FORE AND AFT ALONGTHE TOP OF THE HEAD OF A PERSON SUBSTANTIALLY FROM THE FOREHEAD TO THEBASE OF THE SKULL AND LIMITED IN ITS LATERAL EXTENT TO OMIT COVERAGE OFTHE EARS AND SIDES OF THE HEAD, AND MEANS FOR HOLDING SAID STRIP INPOSITION.